Modern turbines often operate at extremely high temperatures. The effect of temperature on the turbine blades and/or stator vanes can be detrimental to the efficient operation of the turbine and can, in extreme circumstances, lead to distortion and possible failure of the blade or vane. In order to overcome this risk, high temperature turbines may include hollow blades or vanes incorporating so-called impingement tubes for cooling purposes.
These so-called impingement tubes are hollow tubes that run radially within the blades or vanes. Air is forced into and along these tubes and emerges through suitable apertures into a void between the tubes and interior surfaces of the hollow blades or vanes. This creates an internal air flow for cooling the blade or vane.
Normally, blades and vanes are made as precision castings having hollow structures in which impingement tubes are inserted for impingement cooling of an impingement cooling zone of the hollow structure. Problems arise when a cooling concept is used in which a temperature of a cooling medium for the impingement cooling zone is too high for efficient cooling of the latter.
This is known from a cooling concept, where a combined platform and aerofoil cooling systems are arranged in series. A compressor discharge flow feeds in the platform cooling and then passes into the aerofoil cooling system.